The present invention is directed to signal treating devices, such as by way of example and not by way of limitation signal amplifiers, and especially to signal treating devices capable of utilizing substantially all of a supply-voltage range for input and output signal operations. Such use of substantially all of a supply-voltage range is sometimes described as rail-to-rail operation.
Constancy of transconductance (gm) over an operating range is important to ensure consistency of performance for a signal treating device, such as by way of example and not by way of limitation an operational amplifier.
In today's marketplace one encounters signal treating devices such as signal amplifiers and differential signal amplifiers that are provided a supply-voltage range on the order of, for example, 2.7 volts or 3 volts. It is desirable that such signal treating devices be able to effect rail-to-rail operation so that signal-to-noise ratio may be maximized while maintaining a substantially constant transconductance (gm) over an operating voltage range.